Paleolimnology and trends in the phosphorus and iron budgets of an old man-made lake, Barton Broad, Norfolk

SUMMARY. Barton Broad, Norfolk is a shallow, eutrophic lake. During the last 30 years submerged macrophytes have declined and phytoplankton numbers have increased. This change is traced through the stratigraphy of a 60-cm mud core. Diatom frustule counts of 1-cm sections of the core showed that an epiphyte-dominated diatom community was replaced by a planktonic community. From chemical analysis and radio-isotope dating of the core, sedimentation rates and past phosphorus and iron loadings are estimated. Sedimentation rates were between 1.2 mm and 3.1 mm year⁻¹ during the early part of the core but doubled in the 1950s to 5 mm year⁻¹, doubled again in the 1960s and have increased to 12 mm year⁻¹ in the 1970s. Retention of phosphorus in the sediment increased from 0.5 g m⁻² year⁻¹ to 18–21 g m⁻² year⁻¹ in two steps. A similar trend is shown for iron. The diatom species composition and chemistry of the core sections are correlated with increased nutrient loading and the decline of macrophytes. Contemporary phosphorus and iron budgets are calculated from inflow–outflow data and balanced using sediment retentions estimated from the core data. It is believed a large proportion of phosphorus and iron enters the Broad by movement of sediment along the river bed. A reduction of 25% of the 1975 phosphorus loadings would probably permit re-establishment of some macrophytes. The present chemistry and algal communities of Barton Broad and the River Ant are described.     

Protein sequence evidence for monophyly of the carnivore families Procyonidae and Mustelidae

The amino acid sequence of the eye lens protein alpha-crystallin A of the ring-tailed cat, Bassariscus astutus, has been determined. The sequence of the Bassariscus alpha A chain, which is 173 residues long, was compared with the previously determined set of 41 mammalian alpha A sequences. Among the investigated carnivores (dog, cat, sloth bear, American mink, gray seal, and California sea lion) the Bassariscus alpha A sequence exclusively shares two amino acid replacements with the alpha A chain of the mink, Mustela vison: 7 His----Gln and 61 Ile--- -Val. The Mustela and Bassariscus alpha A sequences differ at only three positions and have no replacements in common with any of the other investigated carnivore alpha A chains. Furthermore, the replacement 7 His----Gln has only been found in three-toed sloth, whereas 61 Ile----Val occurs scattered in three other taxa: pig, rhinoceros, and prosimians. It thus is most parsimonious to join Bassariscus and Mustela--and consequently their respective families, Procyonidae and Mustelidae--as sister groups in the phylogenetic tree of mammalian alpha A sequences.      

The systematics of British larval lampreys

Several taxonomic characters, including the number of trunk myomeres, proportional body measurements and patterns of external and internal pigmentation, have been investigated in populations of ammocoetes belonging to the three species of lampreys found in British rivers. Petromyzon marinus can be readily distinguished by the pigmentary pattern in the tail and on the oral hood, and by the much higher number of trunk myomeres. Although no character can be used to separate with certainty the larvae of Lampetra fluviatilis and Lampetra planeri , significant differences were found between the mean number of trunk myomeres in the two species. Moreover, the values for ammocoetes were virtually identical to those of the respective post-larval stages, at which phase in the life cycle the two Lampetra species are clearly distinguishable. The incidence of pigmentation on the tongue precursor was much higher in larval populations of L. fluviatilis than in those of L. planeri and there was also a difference in the rate of change in the relative length of the trunk and tail. Where comparisons can be made, the results in this paper are in agreement with those of most other European and North American workers. The data differ markedly, however, from that contained in the only other previous detailed systematic study on British larval lampreys, which was subsequently used as the basis for taxonomic keys.     

Immunofluorescence studies of neurofilaments in the rat and human peripheral and central nervous system

Localization of antisera to neurofilament antigens derived from rat peripheral nerve was carried out in tissues of rat and human peripheral and central nervous systems by indirect immunofluorescence. Unfixed and chloroform-methanol-fixed frozen sections of tissues were incubated in purified IgG of the experimental rabbit antisera and subsequently exposed to goat anti-rabbit IgG conjugated with fluorescein isothiocyanate. Control studies were conducted on identical tissue preparations incubated in the same concentrations of nonspecific rabbit IgG or in experimental rabbit IgG absorbed with extracts of rat peripheral nerve containing neurofilament antigen. Extensive immunofluorescence was observed in rat and human peripheral and central nervous systems. The distribution and configuration of immunofluorescence corresponded to neurofilament-rich structural components of these tissues. Prominent immunofluorescence was also noted in neuronal cell bodies of spinal sensory ganglia, especially in perikarya of the large neuronal type. Immunofluorescence of the central nervous system was located predominantly in myelinated axons of the white matter in cerebrum, cerebellum, brain stem, and spinal cord. Less intense immunofluorescence was also seen in neuronal perikarya and in short thin linear processes of grey matter.     

Comparison of photosynthesis and productivity of Gunnera tinctoria Molina (Mirbel) with and without the phycobiont Nostoc punctiforme L.

Abstract. Marked increases in growth and nitrogen content were found with Gunnera tinctoria Molina (Mirbel) plants infected (+ Nostoc ) with the cyanobacterium Nostoc punctiforme L., in comparison to uninfected (— Nostoc ) plants and this was attributed to N₂-fixation by the phycobiont. Whilst host and symbiont can be grown separately, preliminary data indicates that the host plant is reliant on the cyanobacterium to meet its nitrogen requirements because it has little capacity to assimilate nitrate. Although the maximum light-saturated rate of photosynthesis was higher in the + Nostoc plants, there was no reduction in photosynthetic efficiency under lightlimiting conditions, despite marked differences in plant nitrogen status. Differences in photosynthetic rate were implicated as the major reason for the differences in plant productivity. Stomatal conductance was insensitive to changes in plant nitrogen status and did not parallel the variation in photosynthetic rates. The ecological significance of the largely invariant stomatal response and the consequences of differences in water and nitrogen-use efficiencies between + and — Nostoc plants is discussed.     

Studies on l-glutamate in insect haemolymph.

ABSTRACT. The neuromuscular junctions of abdominal body wall muscles of larval Lucilia sericata are mainly superficial, with no glial sheath, and are surrounded by a well-developed subsynaptic reticulum. Injection of l -glutamate into the haemolymph of adult male Locusta migratoria and larvae of Lucilia sericata caused reversible effects on motor activity. These effects were quantified and dose—response curves are presented. The effective concentration of the injected doses is low enough to be physiologically relevant. Injection of l -aspartate into Locusta haemolymph affected motor activity. Injection of l -aspartate into Lucilia larvae produced no detectable effect. Injections combining l -aspartate and l -glutamate into Lucilia larvae had a synergistic effect on the duration of paralysis, compared with the same concentration of l -glutamate injected alone.